解法代码来源 ：https://blog.csdn.net/whdAlive/article/details/81084793

算法来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/implement-trie-prefix-tree 

实现一个 Trie (前缀树)，包含 insert, search, 和 startsWith 这三个操作。

示例:

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple");   // 返回 true
trie.search("app");     // 返回 false
trie.startsWith("app"); // 返回 true
trie.insert("app");   
trie.search("app");     // 返回 true

说明:

• 你可以假设所有的输入都是由小写字母 a-z 构成的。
• 保证所有输入均为非空字符串。

网上找了一些解法

class Trie {

//根节点
private TrieNode root;

/** Initialize your data structure here. */
public Trie() {
//初始化根节点
root = new TrieNode();
}

/** Inserts a word into the trie. */
public void insert(String word) {
TrieNode node = this.root;
//遍历
for(char c: word.toCharArray()){
if(node.children[c-‘a’]==null){
node.children[c-‘a’]=new TrieNode();
}
node = node.children[c-‘a’];
}
node.item = word;
}

/** Returns if the word is in the trie. */
public boolean search(String word) {
TrieNode node = this.root;
//遍历
for(char c:word.toCharArray()){
if(node.children[c-‘a’]==null){
return false;
}
node = node.children[c-‘a’];
}
return node.item.equals(word);
}

/** Returns if there is any word in the trie that starts with the given prefix. */
public boolean startsWith(String prefix) {
TrieNode node = this.root;
//遍历
for(char c: prefix.toCharArray()){
if(node.children[c-‘a’]==null){
return false;
}
node = node.children[c-‘a’];
}
return true;

}
//定义 前缀树节点 的结构
class TrieNode{
//孩子节点，分别记录26个字母
TrieNode[] children = new TrieNode[26];
//当前的节点（叶子节点）对应的单词
String item = “”;
}
}

提交后优秀解法

class Trie {
    private static class TrieNode {
        boolean isExist;
        TrieNode[] nodes;
        TrieNode() {
            isExist = false;
            nodes = new TrieNode[26];
        }
        TrieNode put(char c) {
            if (nodes[c-'a'] == null) {
                nodes[c-'a'] = new TrieNode();
            }
            return nodes[c-'a'];
        }
        TrieNode get(char c) {
            return nodes[c-'a'];
        }
    }

    private TrieNode root;


    /** Initialize your data structure here. */
    public Trie() {
        root = new TrieNode();
    }

    /** Inserts a word into the trie. */
    public void insert(String word) {
        TrieNode curr = root;
        for (char c : word.toCharArray()) {
            curr = curr.put(c);
        }
        curr.isExist = true;
    }

    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode curr = root;
        for (char c : word.toCharArray()) {
            curr = curr.get(c);
            if (curr == null) {
                return false;
            }
        }
        return curr.isExist;
    }

    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode curr = root;
        for (char c : prefix.toCharArray()) {
            curr = curr.get(c);
            if (curr == null) {
                return false;
            }
        }
        return true;
    }
}

每天看一些算法，没有时间去研究，只能学习。